i. Field of the Invention
This invention relates to doctor blade assemblies.
More particularly, it relates to fingers used in such assemblies.
II. Description of the Prior Art
German Offenlegungschrift published May 17, 1974, in the name of Jack F. Brown describes a doctor blade assembly. The described assembly includes a doctor blade pressure plate connecting together an array of spaced-apart pressure fingers in parallel relationship. Each of the fingers has a heavy duty one-piece body having a pair of jaws defining between them a doctor blade receiving slot. One of the jaws of each finger is adapted to be permanently secured to the pressure plate.
It had been customary to machine a finger of this type from bar stock, for example, from a free-machining carbon steel. Such a machined finger is then plated to resist corrosion. Such fingers have provided an excellent heavy duty blade support for doctoring purposes.
It has been found, however, that continued exposure to an acidic or alkaline environment encountered in the doctoring operation will, in time, erode the plating and oxidation will ensue.
The fingers may be machined from bar stock of a non-corrosive material having the other physical and mechanical properties necessary, for example, stainless steel. However, the difficult machining operation makes this method of manufacture too costly to be practical.
Another way of making the finger suggested in the aforementioned publication is by casting. Since it can be readily cast in stainless steel, an excellent non-corrosive finger can be made in this way. However, attempts to modify the structure of the finger, to cut down its bulk and reduce its weight gave rise to an unexpected problem, in that the jaw attached to the pressure plate deflected more than the calculated amount.